Just today, I solo'd Rotunda of Olypmus with a level 28 Posiedon.
War Hammer of Poseidon (Rank 1)
Full Manticore Set (Rank 2)
Posiedon's Crest (Rank 3)
Cloak of Boreas (Rank 3)
Relic of Sacrifice (Rank 3)
Yes, it's not even remotely the most ideal set up, but that's what I used.